Many naturally occurring and synthetic ergolines are known to bind to receptors for the neurotransmitters dopamine, noradrenalin and serotonin and to act as agonists or antagonists at said receptors. Given the breadth of this potential physiological activity, a central challenge lies in the development of therapeutically useful compounds that are sufficiently selective for a single neurotransmitter thus eliminating or reducing unwanted side effects during therapy. For example, this challenge has been met with the introduction of the selective serotonin antagonists methysergide and metergoline for the treatment of migraine and, in more recent years, the dopamine agonists bromocriptine and lisuride for the treatment of Parkinson's disease and hyperprolactinemia. Specifically with respect to serotonin (also known as 5-hydroxytryptamine or 5-HT), the receptors therefor have been divided into two major subtypes, 5-HT.sub.1 and 5-HT.sub.2, based on their relative affinities for [.sup.3 H]serotonin and [.sup.3 H]spiperone, respectively. The present invention discloses therapeutic methods utilizing certain 2,3-dihydroergolines which exhibit selectivity for serotonin receptors of the 5-HT.sub.1 subtype and little or no affinity for the 5-HT.sub.2 subtype, dopaminergic or adrenergic receptors. Said 2,3-dihydroergolines act as serotonin agonists thereby manifesting their physiological effects by an increase in endogenous serotonin activity.